During processes for separating water from solute-filled sources, such as seawater, the removal of water molecules from the raw water supply, to produce purified water generates secondary waste streams. The waste streams have selective solute concentrations variously reaching saturation and even super saturation levels. Such solutes are of both mineral and organic composition. These may deposit as precipitation solids whenever and wherever the water makes its actual separation from the process stream, such as within the matrix of any reverse osmosis (RO) membranes being used for processes. These deposits clog the membranes of RO systems. The periodic cleaning of membrane surfaces thus becomes standard practice to keep flows through the membranes at acceptable flux rates. Chemical cleaning does restore a considerable percentage of the original process rate. However it is inevitable that deteriorating recovery flux rates will result after each cleaning cycle. This will eventually require complete membrane replacement.
Cleaning cycle chemicals do essentially remove much of the inorganic scale accumulations. However many slower accumulations of organic contaminants within such membranes are not removed by cleaning. This is because any formulation strong enough to remove the organics would also be strong enough to attack the organic matrices of the membranes themselves.
It is therefore desirable to prevent organic contaminants from even entering operating membranes in the first place.
The type of organics that invade and plug up a membrane film might be characterized as similar to the slippery, gelatinous slimes that evolve naturally off of fish, seaweed, algae, bacteria, and the like. These have only slight hydrophilic solubilities and will form solidified gels once enough water has left them behind within the membrane. Once dehydrated, the jellied organics become insolubly locked in place with no suitable solubilizing reagents able to remove them.
The invention seeks to alleviate these problems by pretreating the water prior to contact with the membranes to cause much of these organics to settle out from the water stream. This is achieved by creating a growth of fine calcium carbonate [CaCO3] particulates which are absorptive of up to 80% of any soluble natural organics (including brown tannins as exampled in brewed tea or natural brown waters).
The invention makes use of the calcium bicarbonates which are naturally found in the water stream and provides conditioners which use turbulent motion within magnetic or electric fields to rip and separate the hydrogen ions [H+] away from the bicarbonate ions [HCO3−] thus forming temporary increases in the formation of extra carbonate ions [CO3═] in the water.
One form of such a conditioner is shown in an earlier magnetic device (U.S. Pat. No. 4,422,933).
The conditioner in accordance with the present invention is a major improvement on such earlier device. The present invention provides an adjustable-flow magnetic field device. The device further will allow major increases in flow volume capacity. Magnetic devices maintain an advantage with salt water where electrical fields are strongly blocked by water conductivity as compared to magnetic field systems.
The large, though temporary, increases of the carbonate content in the water usually finds enough calcium ion [Ca2+] in most waters to supersaturate the water with respect to forming fine calcium carbonate [CaCO3] scale precipitates. Simple chemical equations, such as below represent these conditioner reactions which may prevail for only about three seconds before the chemistry snaps back to normal pH-controlled ratios:HCO3−→H++CO3═ and CO3═+Ca2+→CaCO3↓
Organic contaminants will be absorbed by the calcium carbonate, (as largely formed into a buoyant suspension of fine particulates. The organic solutes most readily trapped within membranes generally are those most easily captured by the carbonate particulates.
While the absorption of organics on the precipitating calcium carbonate is a highly effective method of removing a large proportion of such organic contaminants, it needs to be recognized that the growth of the carbonate crystals from the water is very much more effective than just contacting or dumping preformed calcium carbonate powder into the flow. The latter merely achieves a limited absorption of organics on the original preformed surfaces of the powder, whereas the active growing of the carbonate from the soluble state absorbs organics at each layer of growing crystal formation as those crystals get assembled. Absorptions thus end up throughout the entire volume of the carbonate crystals, rather than just on the outside surface areas. The result is an increase in capture sites for organics by at least a 100-fold. Additionally, once the problem organics become incorporated within such scale particulates, they no longer have access to enter pore membranes to cause problems, and are further denatured by essential de-watering so that their original problematic qualities of being jelly-like or slimy can no longer be reestablished.
The invention when treating larger seawater flows with enhanced effectiveness, represents more than just a minor improvement in water quality for subsequent reverse osmosis and other applications. Depending somewhat on local raw water contaminant levels and suitable installation and related flow adjustments, large cost efficiencies for desalination, for example, may be expected. Conservatively, sustained membrane flux rates between cleaning cycles could be expected to be at least double, and chemical and associated maintenance costs could be expected to be at least halved, and membrane replacements could be between 3 times to 10 times less frequent.